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Wide Bridges - Longitudinal Joint[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Wide Bridges - Longitudinal Joint
- From: Larry Sandhaas <lws(--nospam--at)netexpress.net>
- Date: Thu, 21 Dec 2000 19:28:40 -0600
Something of an introduction by a new list member. I am a structural engineer working mostly on bridge work in the upper Midwest - Iowa and Illinois. Single Point Interchanges seem to have gained popularity - especially in the south and west, but to a lesser degree in the my part of the country. Why this is, I am not sure. The DOT's seem to be rather conservative in these parts. The single point popularity stems from the lesser land area required when compared to the conventional cloverleaf interchange. The price paid is rather wide bridges to accomodate ramps and turning lanes. I have learned from my company's other offices in the west that wide bridges - say between 150'-250' edge to edge- have been built without a longitudinal expansion joint. I have copies of plans of a bridge in Omaha built in just this fashion. No longitudinal joint, integral abutments and reasonable amounts of transverse deck reinforcement. Obvious maintenance advantages - I hate deck joints. I've been thru too many inspections and replacements of old failed deck joints. Iowa and Illinois DOT policy precludes construction of bridge decks greater than about 100' wide without the longitudinal joint. Great efforts in design have been made to accomodate this policy for many years. Simple question - how is it that other states can build bridges quite wide with what appears to be ordinary flexural reinforcement? I think I know the answer - much of it having to do with traditonal ways of doing things. I've done some "back of the envelope" finite elements to satisfy curiosity, and I can't find any substantial difference between a 100' wide bridge and a 200' wide bridge subjected to transverse temp. strains and full restraint at abutments. What measures are taken in other states to accomodate the building of very wide bridge decks, or similar structures in general? I have a suspect that initial shrinkage stresses could be more of a problem than temperature long term. This could be addressed with a prudent choice of deck pouring sequence. Any comments welcome- Regards- Larry Sandhaas, PE
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